Widely used index may have overestimated drought

For decades, scientists have used sophisticated instruments and computer models to predict the nature of droughts. With the threat of climate change looming large, the majority of these models have steadily predicted an increasingly frequent and severe global drought cycle. But a recent study from a team of researchers at Princeton University and the Australian National University suggests that one of these widely used tools—the Palmer Drought Severity Index (PDSI)—may be incorrect.

The PDSI was developed in the 1960s as a way to convert multiyear temperature and precipitation data into a single number representing relative wetness for each region of the United States. The PDSI, however, does not originally account for potential evaporation, which depends on solar radiation, wind speed and humidity. The new model developed by Justin Sheffield, a hydrologist at Princeton and the lead author of the study, and his team accounts for this deficiency, and is subsequently producing different numbers. Has the reported increase in drought over the last 60 years been overestimated? And what might that mean for the future?